A. Technical Field
The present invention relates to a battery charger in a mobile device, and more particularly, to systems, devices and methods of enhancing battery charge rate and reducing corresponding battery charge time for a battery that is driven and charged up by the battery charger.
B. Background of the Invention
A mobile device normally relies on a stable battery power source such as a lithium battery to provide power for its operation. In order to charge up the battery, an external AC-DC adapter is coupled to a wall outlet, and converts an alternative-current (AC) power of 100-240V to a direct-current (DC) power supply. When the mobile device is coupled to the AC-DC adapter via a hard wire, the battery within the mobile device is thereby charged up under the bias of the DC power supply. The charge time may vary significantly according to the volume of the battery that is used in a specific application. Nevertheless, the batteries in most consumer products may be fully charged within a few hours, and some state-of-the-art cellular phones, tablets or laptop computers may only require a couple of hours to reach a full battery charge.
A switch-mode DC-DC converter is normally incorporated within the mobile device as a switch-mode battery charger. The battery charger converts the DC power supply provided by the AC-DC adapter to a battery charging current, and the battery charging current is used to drive and charge up the battery. The switch-mode battery charger mainly relies on a switching regulator to control internal switching activities of a DC-DC converter core. An inductor is incorporated in the converter core to temporarily store power and release it for subsequent use. When the switching regulator alternates between two control states, the battery is continuously charged up by the power that is either directly provided by the external power source or previously stored in the inductor. In contrast with a linear regulator, such a switching based configuration allows the switch-mode battery charger to reach a much higher efficiency level for energy conversion.
Although the switch-mode battery charger is capable of providing relatively higher efficiency, it is a challenge to identify and maintain operation conditions that correspond to a preferred battery charging condition. The DC power supply provided at the adapter output may not be completely used to drive the battery because of the load-line impedance at the battery charger side. Driving capability and efficiency of the adapter is therefore compromised. Moreover, as other sources, rather than the electrical power, are used to charge the battery, driving capability of the corresponding adapter may drift over time, and is not as stable as the AC-DC adapter. In particular, driving capability of such an adapter may depend upon a load condition that is closely related to the battery state.
In prior art, most switch-mode battery chargers cannot efficiently compensate this drift of adapter driving capability, and therefore, the adapter is either insufficiently or overly driven, rather than being driven substantially under the preferred battery charging condition. It is particularly undesirable to overdrive the adapter, because the adapter output voltage may drastically drop with a minor increase of a corresponding overdrive current. Therefore, the battery charging power could be largely compromised for an overdriven AC-DC adapter. Likewise, an insufficiently driven adapter is also associated with a compromised adapter output power, even though the level of degradation is not as serious as that for the overdriven adapter.
Degradation of the adapter output power directly leads to a lower charge rate and an extended charge time for the battery. Therefore, a need exists to identify and maintain a preferred battery charging condition for a battery charging system associated with a battery in a mobile device, such that power provided by an external power source may be efficiently converted and used to drive and charge up the battery quickly.